Beginning several decades ago, plastic film began to achieve wide spread use in the fabrication of many useful articles, quite often as a replacement for woven fabrics. Early in the development of plastic film as a substitute for woven fabrics, patterns were created by imposing the image of a woven fabric into a film during the process of making the film. Wire screens, along with other mechanical implements, were later employed to create plastic films having various designs. As technology developed, metal rolls having engraved patterns were employed in the production of embossed plastic films which would simulate various designs. During this period of time, the person of ordinary skill in the art who made useful articles from plastic film, typically disposable diapers, covers, water repellent clothing, and the like, worked with the film on machinery and observed or studied its characteristics. Refinements or adjustments in the machinery as well as the material took place in order to produce useful articles from such embossed plastic films on high speed production machinery.
U.S. Pat. No. 3,484,835 which issued in 1969 is directed to a plastic film embossed with a pattern simulating a woven taffeta design and the film had an especially desirable characteristic of edge curl resistance during machine processing into useful articles. Embossed plastic film disclosed in this patent offered significant improvement over the earlier taffeta design which existed in the prior art. The simulated taffeta design disclosed in the above mentioned patent is only an example of many different designs created and employed by film fabricators in their effort to simulate woven fabrics or achieve other various visual appearances and physical properties which were advantageous from a manufacturing or consumer standpoint.
Another one of such many designs is referred to in the art as a matte finish. A matte finish has heretofore been characterized by a rather dull finish on a plastic film with no visually perceptible pattern. Matte finishes have been produced in films by the employment of sand-blasted embossing rollers. With the advancement of technology including new formulations in polymer compositions of the polyolefin type, particularly polyethylene, polypropylene and polybutadiene and their copolymers, the problem of handling various films has become complex. While there is a considerable amount of knowledge available to a person of skill in this art, behaviors of polymers, or their properties under various physical conditions, such as machine stress and other conditions, are not readily understood. One might say the plastic film technology is, indeed, more of an art than a science and experience has proven that problems in this area of the art are not as easily understood or solved owing to the unknown factors in handling such polymeric compositions under machine stress either in the manufacture or fabrication of such polymers into useful articles.
U.S. Pat. No. 4,376,147 which issued in 1983 is directed to an embossed thermoplastic polyolefin film simulating a matte finish having excellent winding characteristics without edge curl, extremely low gloss even on both sides and good tape adhesion values, among other advantages, theretofore unachieved in prior matte films. In contradistinction to the prior art sand-blasted matte films, the film of the U.S. Pat. No. 4,376,147 has an embossed pattern comprising embossed lines or channel-like areas which are parallel to the free lengthwise edges of the film. The embossed lines provide a generally rectangular pattern with parallel and transverse lines numbering within the range of 150 to about 300 lines per inch. Employing such an embossed pattern, the surface of the film appears to the unaided eye as a very dull surface. Up to that point in the state of the art the matte film of the mentioned patent achieved a balance of physical surface characteristics theretofore unachieved in known matte films.
More recently, issued U.S. Pat. No. 4,546,029 is directed to a random embossed thermoplastic polyolefin film simulating a matte or dull finish having excellent roll or winding characteristics and processability without edge curl. Moreover, among its other important attributes, theretofore unachieved in prior art diaper matte films, it has relatively equal tape adhesion on both sides of the random embossed film. This is an important feature in diaper films which enables diapers to be used more effectively and conveniently without tearing the film. The random pattern comprises an asymmetric arrangement of asymmetrically raised bosses and depressed areas on one side of the film, and correspondingly, underlying asymmetrically depressed areas and raised bosses on the opposite side of the film. The asymmetric bosses and depressions are of such height and area on the surfaces of both sides of the film such that the unaided eye of an observer does not detect any pattern in the film, even though it is an embossed random pattern. Such a combination of design and embossed depth had been unachieved in plastic films and, quite surprisingly, a unique balance of physical properties had been obtained.
As evidenced by the above background, production of plastic film has been a continuously improving technology and there are demands for further innovation.